The particular objectives of this project are as follows: 1) a detailed investigation of spinothalamic tract (STT neurones in the lubosacral spinal cord of the cat; b) a quantitative classification of SST neurones on the basis of the results obtained in (a); c) an investigation of neuronal responses to inputs from visceral receptors and their interactions with the somatosensory responses; d) analysis of the presumably preferential distribution within the thalamus of projections of different kinds of STT neurones; e) an investigation of descending influences which modify transmission from spinal cord cells. METHODS: STT neurones will be identified by collision, stimulating (with constant current) respective thalamic nuclei with bipolar concentric electrodes while recording neuronal activity in the lumbar cord grey matter with glass pipettes (3M KCL, 4% pontamine sky blue dye). Natural and electrical stimuli will be applied to peripheral nerves and cutaneous fields. Mechanical stimuli will be quantified with use of an electromechanical stimulator which measures skin indentation. Thermal stimuli to be delivered by a radiant heat stimulator, delivering pulses of warm to noxious heat. Viscerosomatic studies will include cannulation of urinary and gall bladders to record effects of spontaneous contractions and induced distension. At the same time, a reversible spinalization technique (cooling the cord) will be used to study modification of transmission through the STT produced by supraspinal descending systems. Units to be located by microdrive readings and histologically verified by locating pontamine dye spots ejected at recording sites.